In recent years, nudging [1]} has been considered to be a potential way of encouraging people to perform pro-social behavior. This is because it makes it possible to avoid (i) the direct cost of changing people's economic incentives and/or limiting people's action space, (ii) the monitoring costs of determining which choice each individual makes and, possibly, the cost of punishing or rewarding each choice, and (iii) the technical difficulties associated with determining individual choices [2]} so that they are cheap and easily to implement.
